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Homework Help: Gravitational potential energy. Please help

  1. Nov 15, 2007 #1
    Gravitational potential energy. Please help!!!

    1. The problem statement, all variables and given/known data
    A projectile is launched from Earth's surface at a speed of 10 km/s. Find the maximum height it reaches.
    2. Relevant equations
    change in U = -change in K
    U = -GM/r
    3. The attempt at a solution
    GMm/r = 1/2mv^2
    ((6.67x10^-11)(5.98x10^24))/r = 1/2 (10^4m/s)^2
    r = 1.5x10^6 m
    the answer is supposed to be 2.5x10^7 m ???
  2. jcsd
  3. Nov 15, 2007 #2


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    Science Advisor
    Homework Helper

    Are you really taking a potential energy difference? I.e. GMm/(r-r_E) where r_E is the radius of the earth? Or did you post the wrong exponent? I definitely get 7 for the exponent, but I don't get 2.5*10^7.
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